1. Field of the Invention
The present invention relates to an RRAM structure and a method of making the same, and more particularly, to an RRAM structure with improved resistance transformation characteristic and a method of making the same.
2. Description of the Prior Art
A semiconductor memory array structure may include a plurality of interconnected memory cells, such as DRAM, MRAM, FRAM and RRAM. An RRAM stores data using the variable resistance characteristic of a resistive layer.
FIG. 1 is a graph illustrating an I-V curve of an ideal RRAM. As shown in FIG. 1, when an ideal RRAM is in a set state, such as in a Vset voltage, the resistance of the RRAM may vary from a high resistance state to a low resistance state. When an ideal RRAM is in a reset state, such as in a Vreset voltage, as the voltage increases, the current will decrease dramatically. That is, the resistance of the RRAM will vary from a low resistance state to a high resistance state. Generally speaking, the I-V curve of an ideal RRAM in the low resistance state and the high resistance state should not overlap each other.
However, for a conventional RRAM, I-V curves of the low resistance state and of the high resistance state have large variations. Therefore, the I-V curve of the low resistance state may overlap that of the high resistance state, causing difficulty in signal analysis.
Accordingly, an RRAM with improved resistance transformation characteristic is required to provide reliable signal processing.